How can I pipe output from git log in Git Bash?

Question

Reason: I want to compare two arbitrary different commits using a difftool. I know the hashes from a search and I don't want to copy these hashes, thus I am looking for a command that does something like

$ log_str=$(git log --all -S"new_tour <-" --pretty=format:"%h")
$ git difftool -t kdiff3 log_str[1] log_str[2] myfile.txt

I would like to be able to address arbitrary indices - not always 1 and 2
It would be great if the answer also gives a hint, how to figure out, what the structure of log_str is. Is it a character? An array of characters? A list? ... using the Bash.

I found some related help here and here, but I can't make it work.
Now I do:

$ git log --pretty=format:"%h"
3f69dc7  
b8242c6  
01aa74f  
903c5aa  
069cfc5

and

$ git difftool -t kdiff3 3f69dc7 b8242c6 myfile.txt

You want git diff HEAD~1 HEAD ? That's the command you currently have. (Which is the same as git show) — hek2mgl
– hek2mgl, Commented Apr 24, 2018 at 7:56
@hek2mgl No, I want to compare two arbitrary different commits using a difftool and I don't want to copy the hashes... — Christoph
– Christoph, Commented Apr 24, 2018 at 7:57
Use git rev-list rather than git log: it's designed for scripting. — torek
– torek, Commented Apr 24, 2018 at 16:32
@torek: But git rev-list -S"new_tour <-" --pretty=format:"%h" does not work. Did I miss anything? — Christoph
– Christoph, Commented Apr 24, 2018 at 16:38
You had --all above; you'll need that, or HEAD, here (this is one significant difference from git log, which will assume HEAD if not given other revision specifiers to start from). Remove the --pretty argument entirely: rev-list's main job is to list revision hash IDs, so that's what it does by default. — torek
– torek, Commented Apr 24, 2018 at 16:53

hek2mgl · Accepted Answer · 2018-04-27 14:22:09Z

2

I would take a two step approach using a temporary file:

git log --all -S'SEARCH' --pretty=format:"%h" > tmp_out
git diff "$(sed -n '1p' tmp_out)" "$(sed -n '2p' tmp_out)" myfile.txt
rm tmp_out

sed is used to display line 1 and line 2 of the file.

With variables:

search="foo"
index_a="1"
index_b="2"
file="myfile.txt"
git log --all -S"${search}" --pretty=format:"%h" > tmp_out
git diff "$(sed -n "${index_a}p" tmp_out)" "$(sed -n "${index_b}p"  tmp_out)" "${file}"
rm tmp_out

in a bash function:

search_diff() {
    search="${1}"
    index_a="${2}"
    index_b="${3}"
    file="${4}"
    git log --all -S"${search}" --pretty=format:"%h" > tmp_out
    git diff "$(sed -n "${index_a}p" tmp_out)" "$(sed -n "${index_b}p" tmp_out)" "${file}"
    rm tmp_out
}

search_diff "foo" 2 3 myfile.txt

edited Apr 27, 2018 at 14:22

answered Apr 24, 2018 at 8:10

hek2mgl

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5 Comments

hek2mgl Over a year ago

You are welcome but please don't my answer in a way that introduces syntax errors. Feel free to modify it according to your needs, but do not change it in place

Christoph Over a year ago

I am sorry - what went wrong? I checked it on my laptop and everything worked. Otherwise I would not have changed anything...

hek2mgl Over a year ago

which shell are you using?

Christoph Over a year ago

Git bash for Windows

hek2mgl Over a year ago

Not sure what's under the hood of that. In a normal bash a function definition using def, like def foo() is a syntax error. Besides that, I would generally not modify answers more than probably fixing a little syntax error. What you do on your computer is your thing, sure.

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